The image-forming mode of liquid crystal displays or the like requires polarizing elements to be placed on both sides of a liquid crystal cell, and generally polarizing plates are attached thereto. Besides polarizing plates, a variety of optical elements have been used for liquid crystal panels to improve display quality. For example, there are used retardation plates for prevention of coloring, viewing angle expansion films for improvement of the viewing angle of liquid crystal displays, and brightness enhancement films for enhancement of the contrast of displays. These films are generically called optical films.
A protection film is generally attached to the surface of these optical films such that the surface thereof will not be damaged or stained during the manufacturing process or transport until they reach customers. In some cases, such a surface protection film is peeled off after attached to an LCD or the like or is once peeled off, before the same or any other surface protection film is attached. Therefore, the surface protection film has a problem in which when it is peeled off, static electricity can be generated to destroy a circuit of an LCD panel or the like. It also has another problem in which it can have an influence on an array element (TFT driving element) inside an LCD panel, which can further have an influence on the liquid crystal orientation to induce defects. Such problems can occur not only when the surface protection film is peeled off but also when friction occurs between optical films by a manufacturing process or customer's operation.
It is proposed that antistatic properties be imparted to optical films such as polarizing plates in order to sufficiently prevent a malfunction of the liquid crystal display and electrostatic destruction of TFT driving elements or the like. For example, since protective films such as triacetylcellulose films are generally provided on both sides of a polarizer to form a polarizing plate, it is proposed that a triacetylcellulose film for use as a protective film for a polarizer be provided with an antistatic layer (Japanese Patent Application Laid-Open (JP-A) No. 11-90038). However, the case where an antistatic layer is formed on the triacetylcellulose film is not preferred, because the number of processes for forming the protective film can be increased so that the yield can be reduced.
It is also proposed that not only a pressure-sensitive adhesive layer but also an antistatic layer be provided to form a surface protection film for use in optical films. However, the case where the antistatic layer is provided to form the surface protection film is also not preferred, because the number of processes for forming the surface protection film can also be increased so that the yield can be reduced. It is also proposed that an antistatic effect be imparted to a pressure-sensitive adhesive tape itself by adding an antistatic agent to the pressure-sensitive adhesive layer of a general pressure-sensitive adhesive tape (JP-A No. 08-253755 and JP-A No. 09-255932). Such a pressure-sensitive adhesive tape can prevent electrostatic charge directly at a part that will be peeled off and could otherwise be electrically charged. However, the pressure-sensitive adhesive tape has a problem in which the antistatic agent can bleed out to stain the attached material. Since optical films are particularly sensitive to surface contamination, such a pressure-sensitive adhesive tape cannot be applied to surface protection films for use in optical films.